In recent years, development of fluorescent lamp and display has advanced swiftly. With such development, the quantum efficiency has become of interest as an index for more accurately evaluating the performance of a phosphor used for the lamp and display. In general, the quantum efficiency refers to the ratio of the number of photons of fluorescence to the number of photons absorbed by an object to be measured (typically phosphor).
As a typical method for measuring such a quantum efficiency, “Absolute Fluorescent Quantum. Efficiency of NBS Phosphor Standard Samples” by Ohkubo and Shigeta discloses a measurement optical system for the phosphor quantum efficiency. Alternatively to the configuration as disclosed, Japanese Patent Laying-Open Nos. 09-292281 (Patent Document 1), 10-142152 (Patent Document 2) and 10-293063 (Patent Document 3) for example propose configurations and methods for measuring the quantum efficiency.
The quantum efficiency measurement apparatuses according to the above-referenced conventional technologies all use an integrating sphere for trapping fluorescence emitted from an object to be measured (phosphor). Generally, the fluorescence emitted from a phosphor is weak. It is therefore preferable to use an integrating sphere having a smaller diameter in order to enhance the measurement accuracy.
In such an integrating sphere, a baffle is provided for hindering fluorescence emitted from a phosphor and/or an excitation light reflected from the surface of the phosphor from directly entering a detector.    Patent Document 1: Japanese Patent Laying-Open No. 09-292281    Patent Document 2: Japanese Patent Laying-Open No. 10-142152    Patent Document 3: Japanese Patent Laying-Open No. 10-293063    Non-Patent Document 1: Ohkubo and Shigeta, “Absolute Fluorescent Quantum Efficiency of NBS Phosphor Standard Samples,” Journal of the Illuminating Engineering Institute of Japan, The Illuminating Engineering Institute of Japan, 1999, Vol. 83, No. 2, pp. 87-93